4m Spectrograph Folding Flat & Collimator

After passing through the slit and filter(s), the light is deflected at a 90° angle by a Newtonian folding flat, and then hits an on-axis parabolic collimator. The returning collimated beam then passes the folding flat (which now fits into the shadow of the secondary mirror) and goes on to the echelle grating.

Both the folding flat and the collimator have interchangable red and blue optimized optics. The blue optics start to fall off in the red at about 5500Å, while the red optics cut off sharply below 4000Å.

You must specify whether you want to use the red or the blue optics.

Figure 1.Old data showing ratio of red/blue newtonian flat reflectivity. The optics of the blue flat have since been realuminized, so the relative performance may be somewhat different than is shown in the figure.

Figure 2.Old data showing ratio of red/blue collimator reflectivity. The optics of the blue collimator have since been realuminized, so the relative performance may be somewhat different than is shown in the figure.